This invention relates to a method for establishing character frame synchronism between a teletypewriter transmitter and a teletypewriter receiver, wherein the teletypewriter transmission takes place unidirectionally from the transmitter to the receiver and wherein the transmitter sends character signals, actuating signals and operating condition signals. The character signals produced at the transmitter identify the characters, for example, the letters of the alphabet, to be reproduced at the receiver. Each character signal identifying an individual character begins with a start signal, is followed by several information signal elements and ends with a stop signal. The actuating signals are used, for example, for initiating character return, line feed and provide space and line feed information. These actuating signals, likewise, begin with a start signal element and end with a stop signal element. Both the character signals and the actuating signals are binary code signals. The latter are to be contrasted with the analog signals used as operating condition signals; operating condition signals identify two operating conditions of the transmitter. Primarily these signals are used as a continuous start signal and a continuous stop signal. Since these are analog signals, they can be transmitted for any length of time and are not specifically characterized by a particular arrangement of start signal elements and stop signal elements. Because of the start signal elements and stop signal elements of the character signals and the actuating signals, each containing a predetermined constant number of bits and lasting for a specified period of time, the correct character frame can be determined at the receiver. Due to the lack of start signals and stop signals as parts of the operating condition signals, it then becomes difficult to ascertain the correct character frame at the receiver.
It is, therefore, an object of the invention to provide a method for determining the correct character frame during the period of time when operating condition signals are being transmitted and to provide a method for establishing proper character frame synchronism of clock actuated devices in transmitters and receivers of systems of the type described hereinabove.